Pseudomyrmex ant-cleared area around bullhorn acacia tree, Costa Rica. The ants chew away and sting any encroaching plants, clearing an area that may be up to 4 yd (4 m)in radius, as can be seen in this image, in return for food and shelter from the plants.

This is one of the most famous mutualisms of all, the relationship between Pseudomyrmex ants and Acacia trees. The ants defend these small trees against herbivorous insects and vertebrates. The ants also chew away and sting any encroaching plants, clearing an area that may be up to 4 yd (4 m) in radius. In return, the plants give the ants food, such as the yellow Beltian bodies seen here, and nectar from extra-floral nectaries. The Beltian bodies contain proteins and lipids and are produced on the youngest and most delicate leaves. The plants also produce thorns that the ants hollow out for nests.